The present invention relates to an omnidirectional endoscope apparatus having a viewfield covering all around the periphery in the peripheral direction.
An endoscope is effective as an apparatus for observing the inner periphery of a narrow and/or elongated space such as the inside of a cylinder block of an engine and the inside of piping, for example. On the other hand, since a typical endoscope has a limited view field angle, such operation as to turn the endoscope is required for the user in order to observe all around the periphery. In this respect, an omnidirectional endoscope which can receive an incident light from all around the periphery in the peripheral direction and take it into image transmitting means is effective because the user can see all around the periphery at a time. As one example of such an omnidirectional endoscope, an endoscope is known which is equipped with, for example, a conical prism placed at a distal end of its insertion section. A distal end face of a light guide (illumination light transmitting means) occupies a position slightly on the basal end side of the conical prism. An illumination light is radially emitted obliquely forward from this distal end face and illuminates an object to be observed. (See the Japanese Patent Application Unexamined (Laid-Open) Publication No. H10-318727.)
In the above known omnidirectional endoscope, the light guide is fixedly embedded in the insertion section. Accordingly, the positional relation between the distal end face of the light guide and the conical prism is held constant. For this reason, it has such a problem that an image looks dark because when the inside diameter of a space of the object to be observed is small, the illumination light strikes upon the inner peripheral surface of the space more on the basal end side than the view field region, and when the inside diameter of the space is large, the illumination light strikes upon the inner peripheral surface of the space more on the distal end side than the view field region.